There are some non-nucleated polypropylene (PP) grades, for example biaxially oriented polyproplylene (BOPP), where a consistent base-line crystallization temperature is required. In BOPP, changes in crystallization rates may affect several processing variables—the point in the process where the film is quenched (or freezes), the temperature at which the film is successfully oriented, and the amount of orientation that can be achieved under standard processing conditions. If a BOPP film becomes inadvertently nucleated, it is well known in the industry that processing problems may be encountered—chief among these is for the film to tear or split in the machine direction as it is being oriented transversally.
Likewise if an injection molding polypropylene grade becomes inadvertently nucleated, it is possible that the shrinkage characteristics may be altered. Therefore, an injection molded article having demanding dimensional tolerances may shrink too much and fall out of specification if made with the inadvertently nucleated composition.
Similar processing problems and/or physical property problems may exist with a wide variety of part fabrications when the incoming polypropylene becomes inadvertently nucleated if the part fabrication was initially established with non-nucleated polypropylene.
A need therefore exists for additives and processes that can reduce or eliminate any residual nucleation in non-nucleated polypropylene grades.